Irrawaddy may be poisoned by arsenic

Geological map pinpoints fresh areas of contamination in Asia.

Arsenic poisoning can cause skin lesions. Credit: M. Sampson, Resource Dev. Int.-Cambodia

Drinking water in Myanmar’s Irrawaddy delta may be contaminated with high levels of arsenic, a geological map suggests.

Arsenic contamination is a serious problem in several regions of south Asia, most notably Bangladesh, where half of the country’s wells may be polluted. Long-term exposure to arsenic can cause skin lesions and cancer.

A new map of southeast Asia by geologist Michael Berg, of the Swiss Federal Institute of Aquatic Science and Technology in Dübendorf, and his colleagues shows the probability of arsenic contamination in the ground­water, based on geological and soil properties (L. Winkel et al. Nature Geosci. doi:10.1038/ngeo254; 2008). The region is particularly prone to arsenic contamination, Berg says, because of the abundance of large deltas filled with relatively young sediment deposited just 10,000 years ago. Young sediment is more reactive, and so thought more prone to releasing arsenic.

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This geological map of southeast Asia shows the probability of arsenic contamination in the ground­water. Credit: Nature

The map marks several recognized arsenic hotspots, including the Red River and Mekong deltas and the Chao Phraya basin. And it reveals a high probability of arsenic in excess of safe limits in southern Sumatra and the Irrawaddy delta — regions for which few data previously existed.

The models will spur debate because not every­one agrees that soil characteristics accurately reflect the sediment below. Years of weathering could have taken its toll on surface properties, argues John McArthur, a geochemist at University College London. “It’s like asking you to tell me what’s in the basement of your building by looking at the floor plan of your lobby,” he says. But Charles Harvey of the Massachusetts Institute of Technology in Cambridge notes that the sediment’s youthful age means the surface may still hold useful information about the composition below. Berg and his collaborators found that their predictions matched known data 60–75% of the time.

Geologists agree that it would not be surprising to find arsenic in the Irrawaddy delta. A 2002 survey of 25 villages in the region found high levels of arsenic in 67% of the wells examined. That survey covered only a fraction of the 3.5 million inhabitants of the region, Berg notes: “There is an urgent need to have a closer look there.”

Because the arsenic originates in sediment below the surface, Cyclone Nargis, which hit the area in May, is unlikely to have greatly affected the region’s groundwater. The inhabitants of the delta now mainly rely on rainwater as a source of drinking water, says Paul Jawor, a relief worker for Médicins sans Frontières who has recently returned from the region. The wells in the delta are currently mostly used for cleaning and washing, he says.

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Ledford, H. Irrawaddy may be poisoned by arsenic. Nature 454, 263 (2008). https://doi.org/10.1038/454263a

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